docs: def _key_is_sas(key):
          # type: (str) -> bool
          """Determine if key is a sas
          :param str key: key to parse
          :rtype: bool
          :return: if key is a sas
          """
          # keys starting with ? are sas keys as ? is not in the base-64
          # character range
          if key.startswith('?'):
              return True
          else:
              # & is not in the base-64 character range, so technically
              # the presence of this character means the key is a sas. however,
              # perform a stronger check for the sig= parameter.
              tmp = key.split('&')
              if len(tmp) == 1:
                  return False
              elif any(x.startswith('sig=') for x in tmp):
                  return True
          return False